1. Technical Field
The present invention relates to an optical disk inspection device and method, and in particular, relates to defect detection using an RF signal, a tracking error signal, or a focus error signal, for example.
2. Related Art
Heretofore, inspection devices for inspecting the presence or absence of a defect in an optical disk have been proposed. For example, JP 11-86286 A discloses a technique for detecting the presence or absence of failure in an optical disk based on light reflected from the optical disk.
FIG. 9 shows the structure of the prior art described therein. According to the description of the prior art, reference numeral 1 represents a CD-R disk. A spindle motor 2 drives the disk 1 to rotate. A spindle servo circuit 3 controls the drive of the spindle motor 2. An optical head 4 emits a laser beam to be applied to the disk 1, and has a photodetector (not shown) that receives the reflected beam reflected by the disk 1. A head servo circuit 5 controls the focusing and tracking of the laser beam applied to the disk 1, and drives a feed motor 6 to control the thread feed for feeding the optical head 4 in the radial direction of the disk 1. A servo control circuit 7 controls the spindle servo circuit 3 and the head servo circuit 5. An RF signal generation circuit 8 generates a main signal output by adding light reception outputs obtained from specific light receiving elements included in the photodetector in order to generate an RF signal representing a recording signal of the disk 1 from the photodetector of the optical head 4. A reflected light amount detection circuit 9 detects a level of the main signal output generated by the RF signal generation circuit 8 to detect an amount of light reflected by the disk 1. The main signal output generated by the RF signal generation circuit 8 is supplied to the reflected light amount detection circuit 9, and is also supplied to a circuit of a main signal processing system which binarizes the RF signal and decodes the digital data.
A sensor 10 generates a detection output associated with the rotation of the feed motor 6. A switch 11 is used to detect an initial set position of the optical head 4 which is located at an innermost point on the disk 1. A displacement amount detection circuit 12 detects an amount of displacement of the optical head 4 in the radial direction of the disk 1 based on the detection output from the sensor 10 using, as a base point, the position at which the switch 11 is switched. A data creation circuit 13 creates data using the detection output from the reflected light amount detection circuit 9 and the detection output from the displacement amount detection circuit 12 in the form of digital data which can be interpreted by a personal computer A serving as a host, which will be described later. An interface 14 provides matching with the personal computer A.
The personal computer A serving as a host is provided with command generation means 17 for generating a command for making a request to an external storage device connected to a connection terminal 16, and an interface 18 for providing matching with the external storage device. The command generation means 17 generates commands for respectively setting inspection conditions regarding the rotational speed at which the disk 1 is driven, the timing of detection performed by the reflected light amount detection circuit 9 and the displacement amount detection circuit 12, and the thread feed speed of the disk 1 provided by the optical head 4, and the inspection conditions are set by setting means 19, and can be changed as desired through input means 20 such as a keyboard. The personal computer A is further provided with data extraction means 21 for extracting reflected light amount information of the detection output obtained by the reflected light amount detection circuit 9 and disk position information of the detection output obtained by the displacement amount detection circuit 12 respectively as reflected light amount data and position data from the digital data created by the data creation circuit 13, disk failure determination means 22 for determining failure of the disk 1 based on the reflected light amount data extracted by the data extraction means 21, position detection means 23 for detecting a disk position in consideration of the position data extracted by the data extraction means 21 and the rotational speed at which the disk 1 is driven, and display control means 24 for controlling a display 25 connected to the personal computer A in accordance with a determination output from the disk failure determination means 22 and a disk position detection output from the position detection means 23. The position detection means 23 detects a disk position in the radial direction of the disk 1 from which reflected light amount data for use in the determination of disk failure performed by the disk failure determination means 22 is taken based on the position data, which is input, and calculates the rotational speed at which the disk 1 is driven to detect a disk position in the rotational direction of the disk 1 from which the reflected light amount data is taken based on the calculated rotational speed. The disk failure determination means 22 presets reference light amount level data as an average level of a normal reflected light amount level range in which the disk 1 can be determined to be in a normal state, compares the reflected light amount data, which is input, with the preset reference light amount level data, and determines that a failure of the disk 1 has occurred when it detects that a level difference obtained based on the comparison falls outside the normal reflected light amount level range in which the disk 1 can be determined to be in a normal state. Further, the disk failure determination means 22 identifies the location of the failure by retrieving disk position data detected by the position detection means 23, and detecting a disk position at which it is determined that a failure has occurred. A command interpretation circuit 27 interprets commands generated from the personal computer A. An access control circuit 28 controls an access operation in which the trace position of the optical head 4 on a disk is displaced in accordance with a command interpreted by the command interpretation circuit 27.
Further, JP 63-168837 A and JP 2008-165846 A also disclose defect detection techniques.
On the other hand, there is a need to quickly and reliably detect the presence or absence of a defect in an optical disk at, for example, disk rental shops, and in consideration of the circumstances under which users who rent optical disks and play them back use various types of optical disk devices to play them back, it is also desired to inspect the presence or absence of a defect in an optical disk to the extent that it can be ensured that the disk will be capable of being played back even if an optical disk device in which the playback conditions are not set to desirable conditions is used. Suppose that, for example, when a scratch defect is found on an optical disk, one optical disk device is incapable of playing it back due to the defect, but another optical disk device is capable of playing it back in spite of the fact that the defect is present because servo gain and other conditions happen to be set to favorable conditions. Because a user who rents this optical disk will not necessarily use the latter optical disk device to play it back, such an optical disk is in effect a defective optical disk, and should be determined to be unusable (NG).